It is known to use ion exchange resins to selectively adsorb certain ionically charged substances from aqueous systems, the adsorption being the result of ionic forces.
It is also known (U.S. Pat. No. 2,974,178) that soluble, cross-linked, addition polymer resins can be effectively employed to concentrate or separate non-ionogenic compounds in liquid phase from miscible mixtures thereof with other non-ionogenic liquids. The concentration or separation is based on selective or preferential imbibition or absorption by the resin of one of the liquids in the mixture apparently attributable to weak molecular forces rather then to ionic forces. By "preferential absorption," it is meant that the resin absorbs a mixture of the components having a higher concentration of what may be termed the "preferentially absorbed" component than is present in the original liquid mixture applied to the resin.
Such addition polymer resin have low surface areas, from 0.1 to 0.001 square meter per gram of resin, and the action depends on the fact that one of the liquids to be separated from the other has a greater solvent or swelling capacity for the resin. Hence it is preferentially imbibed within the body of the resin.
Many organic compounds cannot be effectively separated by such resins because they lack the capacity to be dissolved in, or to swell, the resin. This is particularly true if the solute is a solid substance, rather than a liquid; and it is also true of organic compounds having in their molecules domains of widely different polarity. Such compounds ordinarily cannot swell or dissolve in the resin mass, and, since many compositions contain no material capable of swelling the resin, the process of the afore-cited patent is of no use in concentrating or separating one component from such a mixture.
U.S. Pat. No. 3,531,463 discloses a process for separating from an aqueous medium of water-soluble substances having hydrophobic and hydrophilic portions in their molecules. These substances are primarily ionogenic and non-halogenated, quite hydrophilic and substantially soluble, in excess of 1000 ppm in aqueous solution. The process involves contacting the aqueous medium with particles of a non-ionogenic, macro-reticular water-insoluble cross-linked polymer of polymerizable ethylenically unsaturated molecules comprising about 2 to 100 weight percent of at least one poly(vinylbenzene) monomer, selected from the group consisting of divinylbenzene, trivinylbenzene, alkyl divinylbenzenes having from 1 to 4 alkyl groups of 1 to 2 carbon atoms substituted in the benzene nucleus, and alkyltrivinylbenzenes having from 1 to 3 alkyl groups of 1 to 2 carbon atoms substituted in the benzene nucleus.
Further, certain resins of the present class, commercially available as Amberlite XAD-4 from the Rohm and Haas Company, Philadelphia, Pa., have been suggested as adsorbents for an aqueous system of phenol and its halogenated derivatives, with regeneration by means of dilute caustic soda. Caustic soda was shown to be an effective regenerant for phenols and other ionogenic organic compounds, owing to the weak adsorption of the ionized form of the solute, which is formed during regeneration. However, such a regeneration process would be of no practical value for the organic compounds treated by the present invention, since the latter are non-ionogenic and cannot be so removed from the resin.
In recent years, increasing notoriety and regulatory attack have been the lot of chemical manufacturers and compounders who have long handily disposed of toxic waste liquids into abutting water bodies. Prominent among these are the manufacturers and compounders of such chlorinated hydrocarbons as DDT, dicofol, aldrin, chlordane and the like, which are widely used as commercial pesticides. The products, the side products, and intermediates of their manufacture are biocidal. The acute mammalian toxicity of these products is high with an LD.sub.50 of less than 5000 being normal and LD.sub.50 of less than 500 not unusual. The toxicity of these materials extends also to other life forms both animal as well as vegetable.
In addition to high toxicity these chlorinated organic compounds are characterized by great persistence in the environment. They are not readily biodegradable and therefore accumulate in the environment and are concentrated in the food chain. As a consequence, increasing amounts of these compounds build up in human and animal tissue. Non-chlorinated pesticides cause lesser problems since despite their toxicity they are more readily biodegradable.
Considerable pressure is now being exerted to minimize or preclude the discharge of these chlorinated, organic compounds.
Industry has made major and expensive anti-stream pollution investments in means to minimize the hazard. One well-accepted technique involves the use of granular activated carbon to treat the subject class of plant effluents. As a commercial system, it is workable but expensive to build and operate. It also leaves much to be desired in adsorption kinetics, which lead to a high pesticide leakage, and hence to a low operating capacity and high operating costs. Furthermore, activated carbon possesses poor regeneration efficiency with chemical regenerants.
The latter requires that external thermal regeneration be employed, which entails a large expense in the construction of a regeneration furnace and associated equipment, and in replacing carbon lost by attrition during thermal regeneration.